1. Field of the Invention
This invention relates to microwave rotary joints, and in particular to a contacting compression journal for improving performance at the electrical interface of a rotor and a stator.
2. Description of Related Art
Rotary joints have a long history of applications for the transfer of microwave signals across a rotating interface. To accomplish the transfer of microwave energy across the rotor and stator of a rotary joint, traditional approaches are to use either a contacting or noncontacting interface. In either case, efficient electrical transfer is necessary to minimize signal loss and also to maximize isolation in multiple channel rotary joints.
Noncontacting rotating interfaces employ overlapping longitudinal sections, known as chokes, sized to an axial dimension that is ideal for a particular frequency. Chokes are sized to correspond to the quarter wavelength of a particular frequency and thereby achieve containment of the signal without physical contact at the rotating junction. The advantage of a noncontacting interface is that all physical wear is eliminated. Disadvantages of this approach are size and weight, particularly at lower frequencies, which have longer wavelengths and therefore require longer chokes.
Contacting rotating interfaces traditionally use journals at the electrical junction. Such journals provide a contact of conductive materials at the rotor/stator interface in order to form an electrical short and minimize signal loss. The advantage of a contacting journal is that size can be greatly reduced when compared to a ¼ wavelength choke interface. Disadvantages of the contacting journal are increased torque, the need for a tight and perfectly concentric fit of the rotating interface, and the fact that contact stress in rotation causes wear and ultimate electrical failure at the rotating interface.
Microwave energy in a rotary joint propagates along a cylindrically shaped conductive path. In order to continue a cylindrical path at the rotating interface the contact fit of a journal is driven radially to form a tight contacting transition, which is necessary for efficient transfer of the energy. Traditional journals consist of overlapping cylinders or sleeves sized such that the outer diameter of the inner sleeve contacts the inner diameter of the outer sleeve along a certain axial distance. Electrical performance of a journal is reliant on precise alignment of the interface and subsequent retention of the alignment as the rotary joint wears through use. Precise alignment of the journal interface is difficult and has limited the use of contacting rotary joints, despite significant advantages of size and weight.